feat(models): add Claude Fable 5.1 and correct Sonnet 5 pricing

Register `claude-fable-5-1` in the CLIProxy model catalog, the dashboard
catalog, and the usage pricing registry.

Pricing is taken from Anthropic's official pricing page:

- Fable 5.1 base rates are $10/$50 per MTok with a $12.50 5m cache write,
  matching Fable 5.
- Cache hits bill at 0.025x base input ($0.25/MTok) rather than the
  standard 0.1x multiplier. Anthropic applies that reduced rate only to
  Fable 5.1 and Mythos 5.1, so this entry cannot derive its cache rates
  from CACHE_READ_MULTIPLIER.

This also corrects Claude Sonnet 5 from $3/$15 to $2/$10 (cache write
$2.50, cache read $0.20). The launch introductory rate became the
standard price and the increase scheduled for 2026-09-01 was cancelled,
so the previous entry over-reported Sonnet 5 usage cost by 50%.

Thinking on Fable 5.1 is always on and can only be steered through
effort levels, so the catalog entry exposes the same `low`..`max` level
surface as Fable 5 and Opus 5 instead of a manual token budget.

The GitHub Copilot catalog is deliberately left unchanged, since Copilot
availability for Fable 5.1 is not verified; surfacing it there would
offer a model the backend may reject.

Regenerates docs/reports/hardening-inventory.{json,md} so the ci-parity
gate matches the source tree.

docs/reports/hardening-inventory.json

@@ -739,7 +739,7 @@
         },
         {
           "file": "src/web-server/model-pricing.ts",
-          "loc": 1127
+          "loc": 1138
         },
         {
           "file": "src/cliproxy/config/generator.ts",
@@ -778,8 +778,8 @@
           "loc": 939
         },
         {
-          "file": "src/cliproxy/accounts/registry.ts",
-          "loc": 871
+          "file": "src/cliproxy/model-catalog.ts",
+          "loc": 884
         }
       ]
     }

docs/reports/hardening-inventory.md

@@ -93,7 +93,7 @@ Scope: `src/**/*.{ts,tsx,js,jsx,mjs,cjs}`
 | `src/web-server/routes/cliproxy-auth-routes.ts` | 1531 |
 | `src/cliproxy/auth/oauth-handler.ts` | 1510 |
 | `src/cursor/cursor-executor.ts` | 1234 |
-| `src/web-server/model-pricing.ts` | 1127 |
+| `src/web-server/model-pricing.ts` | 1138 |
 | `src/cliproxy/config/generator.ts` | 1109 |
 | `src/cliproxy/auth/oauth-process.ts` | 1048 |
 | `src/cliproxy/config/env-builder.ts` | 1045 |
@@ -103,5 +103,5 @@ Scope: `src/**/*.{ts,tsx,js,jsx,mjs,cjs}`
 | `src/cliproxy/quota/quota-manager.ts` | 954 |
 | `src/web-server/services/codex-dashboard-service.ts` | 940 |
 | `src/glmt/glmt-proxy.ts` | 939 |
-| `src/cliproxy/accounts/registry.ts` | 871 |
+| `src/cliproxy/model-catalog.ts` | 884 |
 

src/cliproxy/__tests__/thinking-validator.test.ts

@@ -60,6 +60,14 @@ describe('Thinking Validator', () => {
       expect(result.warning).toBeUndefined();
     });
 
+    it('should treat max as a distinct top tier on Claude Fable 5.1', () => {
+      // Fable 5.1 has always-on adaptive thinking steered only by effort level.
+      const result = validateThinking('claude', 'claude-fable-5-1', 'max');
+      expect(result.valid).toBe(true);
+      expect(result.value).toBe('max');
+      expect(result.warning).toBeUndefined();
+    });
+
     it('should treat max as a distinct top tier on Claude Fable 5', () => {
       // Fable 5 shares Opus 4.8's adaptive thinking surface; max must remain
       // distinct from xhigh.

src/cliproxy/model-catalog.ts

@@ -531,10 +531,27 @@ export const MODEL_CATALOG: Partial<Record<CLIProxyProvider, ProviderCatalog>> =
         },
         extendedContext: true,
       },
+      {
+        id: 'claude-fable-5-1',
+        name: 'Claude Fable 5.1',
+        description: 'Most powerful model (1M context, 128K output)',
+        contextWindow: 1000000,
+        nativeImageInput: true,
+        // Thinking is always on and cannot be disabled: Anthropic rejects both
+        // `thinking.type: "disabled"` and manual budget_tokens with 400. Depth is
+        // steered only through effort levels (default `high`).
+        thinking: {
+          type: 'levels',
+          levels: ['low', 'medium', 'high', 'xhigh', 'max'],
+          maxLevel: 'max',
+          dynamicAllowed: true,
+        },
+        extendedContext: true,
+      },
       {
         id: 'claude-fable-5',
         name: 'Claude Fable 5',
-        description: 'Most powerful model',
+        description: 'Previous most powerful model',
         contextWindow: 1000000,
         nativeImageInput: true,
         // New tier above Opus. Same adaptive-thinking surface as Opus 4.8:

src/web-server/model-pricing.ts

@@ -216,20 +216,21 @@ const PRICING_REGISTRY: Record<string, ModelPricing> = {
     cacheCreationPerMillion: 3.75,
     cacheReadPerMillion: 0.3,
   },
-  // Claude Sonnet 5 ($3/$15) — latest Sonnet; shares the standard Sonnet rates.
+  // Claude Sonnet 5 ($2/$10) — the launch introductory rate is now the standard
+  // price; Anthropic cancelled the scheduled 2026-09-01 increase to $3/$15.
   // Registered explicitly so it is a known model rather than relying on the
-  // unknown-model fallback that coincidentally matches these rates.
+  // unknown-model fallback.
   'claude-sonnet-5': {
-    inputPerMillion: 3.0,
-    outputPerMillion: 15.0,
-    cacheCreationPerMillion: 3.75,
-    cacheReadPerMillion: 0.3,
+    inputPerMillion: 2.0,
+    outputPerMillion: 10.0,
+    cacheCreationPerMillion: 2.5,
+    cacheReadPerMillion: 0.2,
   },
   'claude-sonnet-5-thinking': {
-    inputPerMillion: 3.0,
-    outputPerMillion: 15.0,
-    cacheCreationPerMillion: 3.75,
-    cacheReadPerMillion: 0.3,
+    inputPerMillion: 2.0,
+    outputPerMillion: 10.0,
+    cacheCreationPerMillion: 2.5,
+    cacheReadPerMillion: 0.2,
   },
   // Claude 4 Opus ($15/$75)
   'claude-4-opus-20250514': {
@@ -360,6 +361,16 @@ const PRICING_REGISTRY: Record<string, ModelPricing> = {
     cacheCreationPerMillion: 12.5,
     cacheReadPerMillion: 1.0,
   },
+  // Claude Fable 5.1 ($10/$50) — same tier and base rates as Fable 5, but cache
+  // hits are billed at 0.025x base input ($0.25/MTok) instead of the usual 0.1x.
+  // Anthropic applies that reduced multiplier only to Fable 5.1 and Mythos 5.1,
+  // so this entry cannot use CACHE_READ_MULTIPLIER-derived rates.
+  'claude-fable-5-1': {
+    inputPerMillion: 10.0,
+    outputPerMillion: 50.0,
+    cacheCreationPerMillion: 12.5,
+    cacheReadPerMillion: 0.25,
+  },
 
   // ---------------------------------------------------------------------------
   // OpenAI Models - Source: better-ccusage

tests/unit/model-pricing.test.ts

@@ -277,12 +277,24 @@ describe('model-pricing', () => {
       expect(fable5.cacheReadPerMillion).toBe(1.0);
     });
 
+    it('should return correct pricing for Claude Fable 5.1', () => {
+      // Same base rates as Fable 5, but cache hits bill at 0.025x base input
+      // ($0.25/MTok) rather than the standard 0.1x multiplier.
+      const fable51 = getModelPricing('claude-fable-5-1');
+      expect(fable51.inputPerMillion).toBe(10.0);
+      expect(fable51.outputPerMillion).toBe(50.0);
+      expect(fable51.cacheCreationPerMillion).toBe(12.5);
+      expect(fable51.cacheReadPerMillion).toBe(0.25);
+    });
+
     it('should return correct pricing for Claude Sonnet 5', () => {
+      // The $2/$10 launch introductory rate became the standard price; the
+      // scheduled 2026-09-01 increase to $3/$15 was cancelled.
       const sonnet5 = getModelPricing('claude-sonnet-5');
-      expect(sonnet5.inputPerMillion).toBe(3.0);
-      expect(sonnet5.outputPerMillion).toBe(15.0);
-      expect(sonnet5.cacheCreationPerMillion).toBe(3.75);
-      expect(sonnet5.cacheReadPerMillion).toBe(0.3);
+      expect(sonnet5.inputPerMillion).toBe(2.0);
+      expect(sonnet5.outputPerMillion).toBe(10.0);
+      expect(sonnet5.cacheCreationPerMillion).toBe(2.5);
+      expect(sonnet5.cacheReadPerMillion).toBe(0.2);
     });
 
     it('should return Opus-tier pricing for Claude Opus 5', () => {
@@ -430,7 +442,7 @@ describe('model-pricing', () => {
         cacheReadTokens: 1_000_000,
       };
       const cost = calculateCost(usage, 'claude-sonnet-5');
-      expect(cost).toBe(22.05); // 3 + 15 + 3.75 + 0.3
+      expect(cost).toBe(14.7); // 2 + 10 + 2.5 + 0.2
     });
 
     it('should calculate fast-tier Claude Opus 4.8 cost (2x premium)', () => {

ui/src/lib/model-catalogs.ts

@@ -977,10 +977,22 @@ export const MODEL_CATALOGS: Record<string, ProviderCatalog> = {
           haiku: 'claude-haiku-4-5-20251001',
         },
       },
+      {
+        id: 'claude-fable-5-1',
+        name: 'Claude Fable 5.1',
+        description: 'Most powerful model',
+        extendedContext: true,
+        presetMapping: {
+          default: 'claude-fable-5-1',
+          opus: 'claude-fable-5-1',
+          sonnet: 'claude-sonnet-5',
+          haiku: 'claude-haiku-4-5-20251001',
+        },
+      },
       {
         id: 'claude-fable-5',
         name: 'Claude Fable 5',
-        description: 'Most powerful model',
+        description: 'Previous most powerful model',
         extendedContext: true,
         presetMapping: {
           default: 'claude-fable-5',

ui/tests/unit/ui/lib/preset-utils.test.ts

@@ -22,6 +22,7 @@ describe('claude preset utils', () => {
 
     expect(claudeCatalog.defaultModel).toBe('claude-sonnet-5');
     expect(ids).toContain('claude-sonnet-5');
+    expect(ids).toContain('claude-fable-5-1');
     expect(ids).toContain('claude-fable-5');
     expect(ids).toContain('claude-opus-5');
     expect(ids).toContain('claude-opus-4-8');